1. Field of the Invention
The present invention relates to a bubble separator. More specifically, the present invention relates to a bubble separator with a compact and simple structure, which is capable of improving a bubble separation efficiency even when there are bubbles of various sizes contained in a fluid. The bubble separator according to the present invention is used in a lubrication system of an internal combustion engine, and is also applicable to food, paint, and other fields.
2. Description of the Related Art
Dry sump and wet sump systems are commonly known as modes for lubricating internal combustion engines. The dry sump system is a type in which engine oil collects in an oil tank and the engine oil is sent under pressure from the oil tank through a feed pump to lubricate respective parts of the engine. Oil that falls into an oil pan is then returned to the oil tank through a scavenge pump. The wet sump system is a type in which engine oil is intaken from the oil pan by a pump and sent under pressure to lubricate respective parts of the engine. Oil that has finished lubricating then falls of its own accord into the oil pan of the engine.
However, in the dry sump system a considerable amount of air bubbles are mixed into the oil while it is being returned to the oil tank via the scavenge pump. The bubbles contained in the oil are subsequently separated by an oil filter or the like, but there is a risk of poor lubrication due to incomplete separation.
On the other hand, in the wet sump system only a relatively small amount of air bubbles are mixed into the oil, and some bubbles are further eliminated by the pressure of the pump. As a consequence, there is little risk of poor lubrication. However, there have been calls to reduce the size of the pump in order to improve fuel consumption performance. In such case, there is a risk that poor lubrication may occur because air bubbles have not been sufficiently eliminated.
Thus, the bubble fraction of oil must be decreased regardless of whether the lubrication system of the internal combustion engine is a dry sump system or wet sump system.
Hence, to solve the above problems a centrifugal separation type of bubble separator has been proposed for removing bubbles contained in the oil (see Patent Documents 1 and 2 for examples).
Patent Document 1 discloses a centrifugal separator type of bubble removing device formed from a swirl chamber of a predetermined shape and a bubble removing pipe that runs through an end of the swirl chamber along a central axis of the swirl chamber.
Patent Document 2 discloses that a ring-like preliminary spiral flow path is formed on an outer peripheral side of an upper end of a cone-shaped container. Within this preliminary spiral flow path, oil swirls around an axial center of the container so as to join minuscule air bubbles contained in the oil, after which the swirl is introduced into the container where centrifugal separation is performed.
However, in the above Patent Documents 1 and 2, the ratio of bubbles and fluid introduced into the bubble separator may differ depending on the pump discharge flow and amount of flow into the upper oil pan. If the bubbles are many or large, gas is carried towards the fluid discharge holes. But if there is little gas, then the fluid is blown away from the gas discharge holes. In other words, many or large bubbles makes full separation of the bubbles and the fluid difficult as some bubbles are discharged together with the fluid. As a consequence, efficient bubble separation cannot be achieved.
Patent Document 1: Japanese Patent Application Publication No. JP-A-H05-296018
Patent Document 2: Japanese Patent Application Publication No. JP-A-H07-39702